NASA feels 'plutonium pinch' earlier than expected

Many spacecraft are powered by the radioactive decay of plutonium-238, but the US no longer produces the material. Instead, NASA relies on its shrinking stockpile, topped up with purchases from Russia.

Previous estimates suggested the decline would not affect solar-system exploration until after 2020, but NASA is already tightening its belt. Candidates for NASA's next "New Frontiers" mission, which aims to launch an exploratory spacecraft by 2018, will not be allowed to rely on plutonium for power, effectively limiting the candidate probes to solar power only.

That puts a number of destinations off-limits, says Jim Green, head of NASA's planetary science division. These include targets beyond Jupiter or even darkened regions closer to the sun, like the polar regions of Mars. "Without the plutonium, there's just a huge dimension of science we're going to be missing," Green told New Scientist.

NASA is also relying on Russia for some plutonium-238 that it needs for its next major mission to the outer solar system – to explore Jupiter and its moon Europa. The US Department of Energy is currently analysing what will be required to restart plutonium-238 production, but new fuel may not be ready in time for the mission to launch as planned in 2020.

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Plutonium-238's high heat-production rate and 89-year half-life makes it a good power source for long space missions (Image: US Department of Energy)